feat(marketing-pages): sendWelcomeEmail job + handler enqueues it

sendWelcomeEmailJob takes IMailerService, validates the typed input
(userId + email), and delegates to mailer.sendWelcome. The
onAuthUserSignedUpHandler now takes IJobQueue and enqueues
"marketing-pages.send-welcome-email" with the event payload.

Both binders bind a RecordingMailerService at the IMailerService
symbol (production placeholder until a real adapter ships) and pass
mailer / queue into the wrapped factories. Dev-seed additionally
queue.register()s the slug so the in-memory queue dispatches via
the wrapped job; production relies on the generated Payload event-task
to resolve the wrapped handler from the container.

packages/marketing-pages/src/events/handlers/on-auth-user-signed-up.handler.test.ts

@@ -1,15 +1,25 @@
 // packages/marketing-pages/src/events/handlers/on-auth-user-signed-up.handler.test.ts
 import { describe, it, expect } from "vitest";
+import { RecordingJobQueue } from "@repo/core-testing/instrumentation";
 import { onAuthUserSignedUpHandler } from "@/events/handlers/on-auth-user-signed-up.handler";
 
 describe("onAuthUserSignedUpHandler", () => {
-  it("returns a function (factory shape)", () => {
-    const handler = onAuthUserSignedUpHandler();
-    expect(typeof handler).toBe("function");
-  });
+  it("enqueues marketing-pages.send-welcome-email with userId + email", async () => {
+    const queue = new RecordingJobQueue();
+    const handler = onAuthUserSignedUpHandler(queue);
 
-  it("does not throw on a valid stub event", async () => {
-    const handler = onAuthUserSignedUpHandler();
-    await expect(handler({} as never)).resolves.toBeUndefined();
+    await handler({
+      userId: "u-42",
+      email: "alice@example.com",
+      signedUpAt: "2026-05-08T12:00:00.000Z",
+    });
+
+    expect(queue.enqueued).toHaveLength(1);
+    expect(queue.enqueued[0]).toEqual(
+      expect.objectContaining({
+        taskSlug: "marketing-pages.send-welcome-email",
+        input: { userId: "u-42", email: "alice@example.com" },
+      }),
+    );
   });
 });

packages/marketing-pages/src/events/handlers/on-auth-user-signed-up.handler.ts

@@ -1,14 +1,16 @@
 // packages/marketing-pages/src/events/handlers/on-auth-user-signed-up.handler.ts
 import type { UserSignedUpEvent } from "@repo/auth";
+import type { IJobQueue } from "@repo/core-shared/jobs";
 
 export type IOnAuthUserSignedUpHandler = ReturnType<
   typeof onAuthUserSignedUpHandler
 >;
 
 export const onAuthUserSignedUpHandler =
-  () =>
-  async (_event: UserSignedUpEvent): Promise<void> => {
-    // TODO: implement the reaction. Inject dependencies via the factory's
-    // constructor and use them here. The handler runs inside the consumer's
-    // span+capture sandwich, so just throwing on failure is the right shape.
+  (queue: IJobQueue) =>
+  async (event: UserSignedUpEvent): Promise<void> => {
+    await queue.enqueue("marketing-pages.send-welcome-email", {
+      userId: event.userId,
+      email: event.email,
+    });
   };